1. Field of the Invention
The present invention relates to a semiconductor device that transmits and receives data using radio signals. In addition, the present invention relates to an external communication device that transmits and receives radio signals to/from the semiconductor device. Further, the present invention relates to a wireless system that includes the semiconductor device and the communication device.
2. Description of the Related Art
In recent years, a compact semiconductor device (hereinafter referred to as a semiconductor device, and also referred to as an RFID tag, wireless tag, ID tag, RF tag, or wireless chip) that is a combination of an ultra compact IC chip and an antenna for wireless communication has received a lot of attention. Data can be written to and read from the semiconductor device through transmission and reception of communication signals to/from an external communication device (hereinafter referred to as a communication device, and also referred to as a reader-writer, reader/writer, controller, or interrogator).
As an application field of the semiconductor device that transmits and receives data using radio signals, merchandise management in the distribution industry is given as an example. At present, merchandise management utilizing barcodes is the main stream; however, since barcodes are read optically, data cannot be read when there is an interrupting object. On the other hand, since the wireless data transmission method using a wireless communication device reads data of a semiconductor device by radio, the data can be read even when there is an interrupting object. Consequently, an improvement in efficiency, reduction in cost, and the like of merchandise management are expected. In addition, the semiconductor device is expected to be widely applied, such as to train tickets, airplane tickets, and automatic resets (for example, refer to Japanese Published Patent Application No. 2000-149194). In this manner, a system, which identifies or manages persons or objects with the use of a compact semiconductor device that transmits and receives data by radio communication, is called RFID (radio frequency identification), and is attracting attention as a fundamental technology of the IT society.